The present invention relates to a composition for a joint compound for use in filling and coating joints between adjacent panels of gypsum wallboard. More specifically, the present invention relates to compositions of drying type joint compound having reduced water content for decreasing shipping costs.
In the construction of buildings, one of the most common elements is gypsum wallboard, often known as drywall, used in the construction of walls and/or ceilings. Walls made from gypsum wallboard are traditionally constructed by affixing the panels to wood studs or metal framing, and treating the joints between adjoining panels with a specially prepared adhesive called a joint compound. The side edges of the drywall panels are tapered, thus allowing the joint compound to be applied to the seam, between adjoining panels, in such a way that a monolithic surface is created when finished. This process generally proceeds by placing a taping joint compound within the joint formed by the abutted edges of the wallboards, and embedding a liquid-permeable paper or fiberglass tape within that compound. When dry (or set), a second coating referred to as a topping joint compound is applied over the joint, which may be subsequently lightly sanded upon drying. A third or finish coat is applied, allowed to dry, and lightly sanded to create a smooth monolithic surface that conceals any indication of where the drywall seams were. Another type of joint compound is an all-purpose grade that may be used for both embedding the joint tape and for applying the finish coats. A patterned or textured effect may be given to the finished wall and joint through the use of special application tools.
There are several categories of joint compounds. Drying type compounds harden through the evaporation of water, whereas setting type joint compounds chemically react with water during the curing process. Setting type joint compounds typically use calcium sulfate hemihydrate, also known as stucco or plaster of Paris, as a base. When water is added to the setting type powder, it reacts with the calcium sulfate hemihydrate via a hydration reaction to form an interlocking matrix of calcium sulfate dihydrate crystals. The interlocking crystal matrix gives the compound increased strength. The benefit of a setting type joint compound over a drying type is the overall strength of the finished joint, resulting in less shrinking and cracking, as well as an independence from having to wait for the joint compound to be completely dry prior to further finishing. Drying type joint compounds have the advantage of ease of use, as they typically come in a ready mixed form, with water being added and mixed by the manufacturer. A third type of joint compound combines the setting action of a calcium sulfate hemihydrate based compound with the ease of use of a ready mixed compound.
The present composition is concerned with drying type joint compounds. Suitable examples of such compounds are disclosed in U.S. Pat. Nos. 6,476,099 and 6,545,066, both of which are incorporated by reference. These products are provided in buckets or tubs in a consistency that is immediately usable by the user (“ready mixed”). At present, conventional weight ready mixed joint compounds having weights greater than 12 lbs/gallon (1437.917 kg/m3) contain approximately 30-40% water by weight, and as much as 50% by volume. As the conventional weight or density of the composition decreases, there is actually more water by weight in the composition. The '099 patent discloses a composition having water as 32% of the weight, and the '066 patent discloses a composition having water as 40% of the weight. While these ready mixed joint compounds have gained wide acceptance due to their convenience of use relative to bagged, powdered products, and they can be used in manufactured form in some applications, water is added by the user at the jobsite in almost all cases. This jobsite addition of water to the ready mixed joint compound is largely due to the preference by professional applicators, of a relatively low viscosity joint compound that is easily spread in thin coats that dry relatively quickly.
However, the relatively heavier composition in ready mix format, compared with dry, bagged joint compound increases the shipping costs for a given sample of joint compound, where the ready mix type is typically provided in one or five gallon containers such as buckets or pails. Due to an increased focus on environmentally friendly technologies, there is a motivation in the industry to reduce the amount of energy expended in the joint compound production and distribution supply chain.